Generally, laminated articles of the aforesaid type are constructed by progressive stamping. When the laminations have been stamped they are stacked, advantageously by the stamping tool itself, and are connected together by coupling elements, also known as "clips", which project from one of the faces of the lamination and are formed by deforming the lamination in particular mutually symmetrical positions.
Specifically, during coupling, the projecting part of the coupling elements of a first lamination is inserted or forced into the recessed part of the coupling elements of a second underlying lamination and so on until the last lamination of the pack is reached, which is generally not provided with projecting coupling elements and instead comprises simple through cavities, to prevent one article gripping another if laid thereon.
Coupling the laminations together in the aforedescribed manner has certain drawbacks. The most important derives from the fact that the clips, formed by stamping a metal lamination, normally have the projecting part dimensionally larger than the recessed part (the projecting profile being determined by the die and the recessed part by the punch).
Consequently it is very difficult to size these two parts to satisfy the clamping requirements of the article as their two shape-generating elements are linked together.
A further drawback derives from the fact that the stamping device for forming the laminated article must include a station dedicated to stamping an end lamination, this increasing the complexity of the dies and hence their cost.
Moreover, laminated articles are generally compensated, i.e., they are constructed in such a manner as to overcome the geometrical and mechanical non-uniformities of the metal strip from which the laminations are punched. For this purpose it is known to rotate each lamination relative to the preceding through a certain angle, known hereinafter as the compensation angle.
In known articles this compensation angle is that between one clip and the next, and is hence related to the number of clips in relation to the geometry of the lamination. For example, for circular laminations the compensation angle is about 60.degree. if six clips are present, about 90.degree. for four clips and about 120.degree. for three clips. The time required to rotate the lamination through the compensation angle considerably affects the construction time for the laminated article. This is particularly valid in the case of progressive stamping devices which also stack the laminations, in which at each die-cutting blow the die containing the laminations to be stacked has to be rotated.
Further drawbacks when using known clips, and in particular finned clips, occur in the case of spiralled laminated articles, for example spiralled rotor packs. In this case, to enable the projecting parts of the clips of one lamination to be inserted into the recessed parts of the next lamination while at the same time enabling the two thus compacted laminations to be slightly rotated, a discharge hole has to be provided in each lamination in correspondence with each clip, this in certain cases, for example in the case of die-cast rotors, giving rise to problems. In this respect, infiltrations of aluminium into such discharge holes have occurred, causing motor malfunction related to the creation of parasitic cages.
It should also be noted that laminated articles in which the laminations comprise clips to be coupled together have been in use for many years, but up to the present time the problem of improving such a coupling system has not arisen.